Proxima B is the closest exoplanet: Could there be life there?
- Proxima B è l'esopianeta più vicino: Potrebbe esserci vita lì?
In 2019 the Parkes Observatory in Australia
detected a strange radio signal that seemed to come from the Alpha Centauri star system; after an
arduous analysis, scientists ruled out that this signal came from outer space since it was most
likely a signal from some artificial satellite. While an extraterrestrial civilization did not
send this signal, it reawakened the enthusiasm of the scientific community to find life
outside our planet, especially since the Alpha Centauri system has the exoplanet Proxima B,
which is quite similar to Earth. Ready? Let's get started!
Let's compare it with Earth to find out what possibilities
there are that life exists in Proxima B. Proxima B has a radius of 1.1 concerning
the Earth and a mass of 1.27 Earth masses; this means that both have very similar size and masses,
only that Proxima B is a little larger; this is also in the habitable zone of its star,
has a surface temperature that oscillates between −39 ° C and has all
the conditions to harbor water on its surface. But the similarities end here. Proxima B does
not orbit a star like a sun but orbits the star Proxima Centauri, a red dwarf type star;
this type of star are characterized because they are not so hot and emit jets
of radiation spontaneously, which can tear the atmosphere of a planet like Proxima B.
In addition, although this exoplanet orbits within the habitable zone, this region is much closer to
its star than our solar system's habitable zone. For example, if we were to place the habitable
zone of Proxima Centauri in our solar system, it would be much closer than the orbit of
Mercury. This means that Proxima B orbits very close to its star, so the effects of
radiation and gravity must be felt intensely, affecting its atmosphere and even its rotation.
Extreme solar flares Unfortunately, any life
that can call that planet home will have a hard time. Proxima Centauri is a red dwarf star with
only a fraction of the mass of the Sun. Because of their small size, the nuclear fusion cores of red
dwarf stars are much closer to their surfaces. This makes their surfaces much more chaotic
than stars like the Sun, and that increased turbulence amplifies powerful magnetic fields.
Those solid magnetic fields can launch powerful bursts of radiation and high-energy particles
into the surrounding system. At distances far enough from a star, this is no big deal.
But because stars like Proxima Centauri aren't as luminous as the Sun,
their habitable zones are much closer. Close enough that "habitable" is too generous a word.
Although astronomers already felt that life on Proxima b would be tough,
they did not know the exact location of the magnetic field around Proxima Centauri. Instead,
they had to rely on observations of similar stars. A new study used high-resolution maps of Proxima
Centauri's magnetic field to develop a model of the solar wind emanating from that star.
They found that, with the most accurate information, the situation is as bleak as
we had thought. Proxima b receives about 1,000 times more solar wind radiation than Earth.
This would make it extremely difficult for the planet to harbor an atmosphere, let
alone liquid water. While it doesn't completely rule out the possibility of life in that world,
it does mean that any life that has arisen there has a much harder time surviving than we do.
Simulations have shown that if Proxima b has an atmosphere or magnetic field similar to Earth's,
then and only then, life on its surface might be possible. But without that protective barrier, any
life on this exoplanet will most likely disappear regularly because of the high radiation levels.
Also, if the planet has a thin atmosphere or no magnetic field, it might not be as
promising a place for life as we expected. Until we can observe the planet more closely,
either ourselves or with a high-powered telescope, we won't have clear answers.
Gravity could play in favor Although the star orbiting Proxima B
emits solar flares, if it has a magnetic field and a dense atmosphere, this could protect the
living beings that lived there; the good news is that this exoplanet could have an atmosphere.
In a new study, an international team of researchers found Proxima
B to be 17% more massive than our planet. Previously, scientists thought that this
exoplanet, which lies in its star's habitable zone, harbored a minimum of around 1.3 Earth
masses. The new measurement indicates that Proxima b could look even more like our home
planet, at least in size, than previous observations led scientists to think.
This means that if it has enough mass, it could also have a gravitational attraction force
so great that it would not let its atmosphere escape, even if there were constant solar flares.
However, this same factor could play against it, since having a lot of mass and at the
same time being so close to its star, Proxima B could present tidal coupling.
Tidal coupling occurs when a celestial body gives the same face at all times to the
body it orbits; an example is the moon which is gravitationally coupled to the Earth; therefore,
we always see the same face of the moon. In the case of Proxima B, the same thing
could happen; this planet could have one of its faces always pointing at its star so that
on one of its sides, it would be eternal at day and, on the other, eternally at night.
Although tidal coupling does not prevent living beings, it would make the presence of life quite
difficult because the atmospheric conditions would be extreme. The side of the exoplanet
that is always pointing at the star would be a hot hell like Venus, while the side that is
in the dark would be frozen entirely; the only area where there could be life would be in the
sunrise strip between the hot and cold zone. This region could have much more pleasant
temperatures and even liquid water, but what is the authentic atmosphere of this planet?
Ocean World For sure, it is not known how the atmosphere
of Proxima B is since it does not pass in front of its star-like other exoplanets that are discovered
through stellar transit; because of this, we can not study its composition and determine
if it has water, oxygen, ice or atmosphere. We know that this exoplanet is very similar
in size, weight, and distance to many other exoplanets found in the galaxy,
so analyzing it with pure statistics indicates that it is an oceanic planet.
The oceanic planets are characterized because they are covered with an ocean of
liquids (including water); if so, this world could host aquatic beings that adapt to the
harsh temperatures avoiding going to the surface and staying permanently in the ocean's depths.
It could also be that if temperatures are low enough, the outermost layer of the exoplanet
freezes, ultimately turning it into a snowball planet, much like the moon of Jupiter, Europa.
Europa is a natural satellite wholly covered in ice, but it is known that there may be an ocean of
liquid water beneath all those thick ice sheets. If Proxima B is a world with similar conditions,
living beings could protect themselves from radiation by taking refuge under the ice sheets of
the exoplanet; in addition, if this world also has volcanism, as with underwater volcanoes on Earth,
living beings could adapt to darkness with bioluminescence and survive without problems
for thousands of years. Acquiring the heat of the seabed and protecting itself from the
radiation under the ice sheets. Different ways of life
Another option that many scientists and astrobiologists propose is that
a new type of different from the Earth could emerge in Proxima B.
Until now, we have always looked for carbon-based life that requires water since that is how life
works on Earth, but it is probable that, on other planets, with entirely different chemistry
and conditions, living beings different from us could arise, with unknown morphology and needs.
In this case, many suggest that with the conditions of Proxima B,
it would be enough for a type of life to emerge that does not require the amounts of
oxygen that we need and that can survive shallow temperatures on the seafloor, adapt and evolve.
Some even speculate that there is no need to invent living beings with different chemistries,
like the silicon-based extraterrestrials that Carl Sagan once imagined; it would be enough if
Proxima B had the minimum conditions to sustain an atmosphere dense enough for extremophiles
bacteria to emerge, which exist here on Earth. These organisms can survive very extreme
environments, from the boiling calderas of geysers to the ice sheets of Antarctica;
if this exoplanet can sustain an environment at least a little similar to those two scenarios,
that would be enough to be able to have living beings in the form of tiny bacteria.
Unfortunately for all scientists and dreamers, we cannot check if
Proxima B has volcanism, atmosphere, or water; for now, everything is an enigma.
As this exoplanet cannot be observed by stellar transit, everything we know about
it has been concluded through simulations; of course, this does not mean that nothing
that has been said is speculation; it simply means that we must wait for technology to
continue advancing to have more information that helps us know what this world is like.
For now, we know that it exists, that it is there waiting for us to discover all its mysteries, and
considering how curious and ambitious the human race is, we will indeed discover it very soon.